DESCRIPTION: The Applicant has observed that calcitriol could enhance 2-O-tetradecanoylphorbol-13-acetate (TPA) - induced tumorigenic transformation of the pre-neoplastic mouse epidermal JB6 line. Treatment of these cells with calcitriol by itself didnot induce cell transformation nor did it lead to phosphorylation of osteopontin (POPN). In contrast she observed that induction of POPN and its secretion correlated with tumorigenesis when the cells were stimulated with TPA or TPA and calcitriol. The Applicant proposes to pursue the mechanisms by which calcitriol enhances TPA induced tumorigenesis. She conjectures that calcitriol enhances TPA-induced tumorigenesis by regulating transcription of a combination of genes including the gene for POPN which confers upon these cells a transformed phenotype. The Applicant proposes four specific aims. These include: the employment of calcitriol analogs with defined functions (i.e., binding to the vitamin D receptor or mediating cellular calcium fluxes) to determine if synergism of calcitriol with TPA arises from genomic and/or nongenomic effects of calcitriol. 2) She plans to determine if calcitriol treatment of her cell line affects TPA induced expression of members of the fos and jun families of protooncogenes as well as enhances the expression of protein kinase C. 3) She plans to develop antisense constructs to the OPN gene to determine whether expression of OPN is necessary for TPA-induced tumorigenic transformation. 4) Finally, she plans to use differential display of MRNA to investigate possible unique gene expression in the cell line treated with TPA and/or calcitriol.